Two Case Studies From a Family With Primary Fanconi Syndrome

We report two cases from a family with primary Fanconi syndrome. A 39-year-old white woman with a history of frequent bone fractures developed hypophosphatemia, hypouricemia, hypokalemia, metabolic acidosis, and renal glycosuria. Her 15-year-old son had renal glycosuria without metabolic acidosis. Both had mildly to moderately impaired renal function. Determination of amino acids in 24-hour urine specimens confirmed the generalized nature of aminoaciduria. Acid-loading, bicarbonate-loading, and phosphate-loading tests revealed that the mother had proximal (type II) renal tubular acidosis and excessive renal loss of phosphate for her level of renal function. These tests for the son were normal or within normal limits of his renal function. Known causes of Fanconi syndrome, such as cystinosis and Wilson's disease, were excluded by slit-lamp eye examination and leukocyte cystine level determination. One unexpected finding in the son was the presence of nephrocalcinosis on x-rays; a percutaneous needle biopsy of the kidney showed tubular atrophy, interstitial fibrosis, and calcium oxalate crystal deposits. The two cases presented here represent a familial variety of the primary Fanconi syndrome, a rare entity with a limited number of cases reported in the literature.